Method of treating the electrolyte in the electrodeposition of iron



1952 E. H. KONRAD ETAL 2,580,681

METHOD OF TREATING THE ELECTROLYTE IN THE ELECTRODEPOSITION OF IRONFiled Aug. 24, 1948 FEED TANK ELEC YTIC TANK LEACH TANK mmmalzxcrmcmm:

FILTER 1 SULPHATE REMOVAL H s REMOVAL This filtrate is accordinglyfurther treated for the elimination and removal of the hydrogen sulphideand colloidal sulphur. This may be completely effected by contacting itwith activated charcoal, either by adding the charcoal to it andagitating, or by passing the solution through a suflicient mass ofactivated charcoal,

and then filtering. The adsorbent charcoal thus.

acquires and retains a high percentage of sulphur, both as free sulphurand as hydrogen sulphide, which may be recovered' As thus completelyliberated from both hydrogen sulphide and free sulphur, the resultingclear, strongly acid solution offerrous chloride (or other ferrous salt)is especially adaptable-to the continued electrodeposition ofelectrolytic iron therefrom.

If the liberated hydrogen sulphide or ,the free sulphur are oxidized, asthey often are during the prolonged leaching treatment or re-cycling ofthe solution, so as to form sulphuric acid or soluble sulphur compoundsin the electrolyte, these may be precipitated as calcium sul phate, bythe addition of calcium chloride to the liquor during the leachingoperation, and subsequently separated. with the coagulated sulphur onthe activated charcoal, or by separate precipitation and filtration. a

The leaching liquor or solution containing hydrogen sulphide andcolloidal sulphur may also be liberated of these components .byagitating with a stream of compressed airor by allowing the solution tostand quiescent for a prolonged period of time (24 to 36 hours)-'followed in either case by filtering out the thus coagulated sulphur.

The filtered, clarified solution of electrolyte,

as diagrammatically shown in the accompanying drawings in which Fig. 1is a diagrammatic flow sheet oi the sequence of process steps; and

Fig. 2 is a diagrammatic showing of supple mentary process steps whichmay be associated and conducted with the steps of Fig. l.

The tank i may contain the initial supply of an aqueous solution of theferrous salt, such as ferrous chloride, or a supply of acid such ashydrochloric acid, or both. The conventional electrolysis tank 2, withdiaphragm 2a and anode 4 defining the anolyte portion, and cathode 3 isprovided with the aqueous electrolyte 5 from tank I (or by recirculationas pointed out below) which is characterized, during electrolysis, bycontaining water, 12% to 20% of iron, in the form of a ferrous salt,such as ferrous chloride, an acid such as hydrochloric acid to a pHvalue of 1.2 to 2.0, and in the cathode portion not more thanapproximately 0.4% of iron in the form of a ferric salt, such as ferricchloride, and in the anode portion approximately 3.5% to 10.0% or ironin the form of a ferric salt such as ferric chloride.

In operation the electrolyte .5 may be withdrawn from the anolyteportion by the pipe 5 and circulated in the leach tank I having an agi-'tator 1a over sulphide iron ore, such as pyrrhotite.

as thus obtained, is then returned to the electrolytic cell, for thecontinued electrodeposition of iron therefrom, and directed either intothe electrolytic bath as a whole .(if a non-diaphragm cell is used, asit may be) or into the catholyte compartment, in the case of a diaphragmcell. It may require some addition of acid to adjust the pH value to thedesired degree of acidity as indicated above. But if sulphuric acid isformed in the leaching operation and the sulphate radical thereofprecipitated by calcium chlorides, this will liberate freehydrochloricacid into the solution, which will in part' or wholly compensate for thelo s of acid due to solvent action of the acid of the solution upon theiron sulphide or the formation of hydrogen sulphide.

This invention accordingly provides a method of leaching sulfide ores orconcentrates containing iron and copper sulfides in varying proportionsand a variety of minor constituent metals in such a manner as toproduce:

1. A solution of iron suitable for the production of smooth deposits ofelectrolytic iron of high purity;

2. A residue containing a high percentage of characterized by containinga sulphide or sulphides of other metals such as of the copper or tingroup, nickel or'cobalt, the ore being fed to the leach tank in aconventional manner. The reduced leach liquor may be drawn off, with orwithout separation from attendant solids. through pipe 8, to the filter9, from which the filtrate may be drawn off by pipe I 0 and led intotank H, for treatment for removal of hydrogen sulphide. e. g., bycontact with activated char coal. The thus treated liquor is then passedthrough pipe I2 to filter 13, to remove the charcoal with adsorbed gasesand colloidal residues, and the resulting filtrate drawn off throughpipe M and conducted back into the cathode portion of the electrolyte 5,as shown.

In the case of oxidized ores or leach liquors which may otherwiseacouire the pre ence of sulphates, as above-described, the leach liquor.after being removed from the ore in leach tank I and passed throu h thefilter 9, may be bypassed from pipe Hi to pipe I5 and thence into tank[6 for treatment with calcium chloride. The resulting mixture then maybewithdrawn through pipe I! to filter I8, the filtered solution then beingreturned through pipe l9 to pipe 10 and thence into the treating tankII.

It should be'understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

We claim:

1. Method of treating the anolyte in the electro-deposition of iron,which anolyte has a pH of 1.2 to 2.0 and contains 35 to grams per literof iron in ferric condition, comprising contacting the anolyte with anexcess of an acid soluble iron sulphide ore containing another metalwhose sulphide is insoluble in said anolyte after the ferric ions havebeen reduced to ferrous ions, such excess of ore being sufiicient tocompletely reduce all ferric iron present in the anolyte to ferrous ironand to subsequently react with the free acid present in the anolyte toform hydrogen sulphide, dissolving the iron and other metals soluble inthe anolyte and continuing the leaching of the ore by the anolyte untilthe ferric iron is completely reduced to ferrous iron and hydrogensulphide is then formed from the free acid and precipitates the othermetal as insoluble sulphide, separating the resulting mixture ofsolution and solids, treating I the solution portion therefrom to removethe hydrogen sulphide and the free sulphur content, and returning theclear solution as catholyte to the electrolytic cell.

2. The method according to claim 1 in which the anolyte has a pH of 1.2to 2.0 and contains 35 to 100 grams per liter of iron as ferric chloride3. The method according to claim 1 wherein separating of the resultingmixture of solution and solids is conducted by filtering the mixtureandtreating the filtrate with activated charcoal I to remove the hydrogensulphide content.

4. The method according to claim 1 wherein separating of the resultingmixture of solution,

and solids is conducted by filtering the mixture and treating thefiltrate with compressed air liter of iron as ferric chloride,comprising con-' tacting the anolyte with an excess of an acid solubleiron sulphide ore containing another metal whose sulphide is insolublein said anolyte after the ferric ions have been reduced to ferrous ions,such excess of ore being suflicient to completely reduce all ferric ironpresent in the anolyte to ferrous iron and to subsequently react withthe free acid present in the anolyte to form hydrogen sulphide,dissolving the iron and other metals soluble in the anolyte andcontinuing the leaching of the ore by the anolyte until the ferric ironis completely reduced to ferrous iron and hydrogen sulphide is thenformed from the free acid and precipitates the other metal as insolublesulphide, separating the resulting mixture of solution and solids,treating the solution portion therefrom with calcium chloride toprecipitate any sulphate ion content in the solution portion, filtering,treating the clear solution to remove hydrogen sulphide, filtering andreturning the clear solution as catholyte to the electrolytic cell.

ERICH H. KONRAD. WARREN H. KAYE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,432,543 Eustis et al Oct. 17,1922 1,456,615 Belcher et a1 May 29, 1923 1,567,916 Conder Dec. 29, 19251,751,099 Pike Mar. 18, 1930 1,945,107 Cain Jan. 30, 1934 1,980,381 CainNov. 13, 1934 2,273,036 Heise et a1 Feb. 17, 1942 2,503,234 Cain Apr.11, 1950 OTHER REFERENCES Filtration and Filters, by J. A. Pichard,1929. pages 28, 374, 405.

1. METHOD OF TREATING THE ANOLYTE IN THE ELECTRO-DEPOSITION OF IRON,WHICH ANOLYTE HAS A PH OF 1.2 TO 2.0 AND CONTAINS 35 TO 100 GRAMS PERLITER OF IRON IN FERRIC CONDITION, COMPRISING CONTACTING THE ANOLYTEWITH AN EXCESS OF AN ACID SOLUBLE IRON SULPHIDE ORE CONTAINING ANOTHERMETAL WHOSE SULPHIDE IS INSOLUBLE IN SAID ANOLYTE AFTER THE FERRIC IONSHAVE BEEN RECUCED TO FERROUS IONS, SUCH EXCESS OF ORE BEING SUFFICIENTTO COMPLETELY REDUCE ALL FERRIC IRON PRESENT IN THE ANOLYTE TO FERROUSIRON AND TO SUBSEQUENTLY REACT WITH THE FREE ACID PRESENT IN THE ANOLYTETO FORM HYDROGEN SULPHIDE, DISSOLVING THE IRON AND OTHER METALS SULUBLEIN THE ANOLYTE AND CONTINUING THE LEACHING OF THE ORE BY THE ANOLYTEUNTIL THE FERRIC IRON IS COMPLETELY REDUCED TO FERROUS IRON AND HYDROGENSULPHIDE IS THEN FORMED FROM THE FREE ACID AND PRECIPITATES THE OTHERMETAL AS INSOLUBLE SULPHIDE, SEPARATING THE RESULTING MIXTURE OFSOLUTION AND SOLIDS, TREATING THE SOLUTION PORTION THEREFROM TO REMOVETHE HYDROGEN SULPHIDE AND THE FREE SULPHUR CONTENT, AND RETURNING THECLEAR SOLUTION AS CATHOLYTE TO THE ELECTROLYTIC CELL.